[/
  Copyright 2011 - 2020 John Maddock.
  Copyright 2013 - 2019 Paul A. Bristow.
  Copyright 2013 Christopher Kormanyos.

  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE_1_0.txt or copy at
  http://www.boost.org/LICENSE_1_0.txt).
]

[section:gmp_rational gmp_rational]

`#include <nil/crypto3/multiprecision/gmp.hpp>`

   namespace boost{ namespace multiprecision{

   class gmp_rational;

   typedef number<gmp_rational >         mpq_rational;

   }} // namespaces

The `gmp_rational` back-end is used via the typedef `nil::crypto3::multiprecision::mpq_rational`.  It acts as a thin wrapper around the [gmp] `mpq_t`
to provide a rational number type that is a drop-in replacement for the native C++ number types, but with unlimited precision.

As well as the usual conversions from arithmetic and string types, instances of `number<gmp_rational>` are copy constructible
and assignable from:

* The [gmp] native types: `mpz_t`, `mpq_t`.
* `number<gmp_int>`.

There is also a two-argument constructor that accepts a numerator and denominator (both of type `number<gmp_int>`).

There are also non-member functions:

   mpz_int numerator(const mpq_rational&);
   mpz_int denominator(const mpq_rational&);

which return the numerator and denominator of the number.

It's also possible to access the underlying `mpq_t` via the `data()` member function of `mpq_rational`.

Things you should know when using this type:

* Default constructed `mpq_rational`s have the value zero (this is the [gmp] default behavior).
* Division by zero results in a `std::overflow_error` being thrown.
* Conversion from a string results in a `std::runtime_error` being thrown if the string can not be
interpreted as a valid rational number.
* No changes are made to the [gmp] library's global settings, so this type can coexist with existing
[gmp] code.
* The code can equally be used with [mpir] as the underlying library - indeed that is the preferred option on Win32.

[h5 Example:]

[mpq_eg]

[endsect] [/section:gmp_rational gmp_rational]
